"With chip makers continuing to increase the number of cores they include on each new generation of their processors, perhaps it's time to rethink the basic architecture of today's operating systems, suggested Dave Probert, a kernel architect within the Windows core operating systems division at Microsoft."

GPUs are specialized for doing parallel arithmetic operations. Specifically, a GPU can perform a vector sum in one cycle, whereas the CPU would require more cycles. The problem with your suggestion is that the kernel doesn't spend most of its time doing vector sums, but instead things like interrupt handling and context switching.

I think that when we are watching flash videos on youtube, listen to mp3s, play movies, using some compression or cryptography software, we make heavy use of SIMD instructions and vector arithmetics. So why not use some GPU muscle?